Question

A lil help would be appreciated!

What is percentage of iron in Mohr’s salt?

What are advantages of potassium dichromate over potassium permanganate?

Answer 1

Mohr's salt is ammonium iron (II) sulfate:\[\color{green}{(NH_4)_2Fe(SO_4)_2\cdot 6H_2O}\]
Divide the mass of the iron (one iron atom per molecule) in this compound by the molar mass of the compound, and multiply by 100 to express it as a percent.

As for your second question, if the two compounds can be used interchangeably, potassium permanganate is a strong oxidizing agent, so in some situations it may be less advantageous to use it.